METHOD OF MAKING TITANIUM ALLOY BASED AND TiB REINFORCED COMPOSITE PARTS BY POWDER METALLURGY PROCESS

ABSTRACT

A method of preparing a titanium-based metal matrix composite. In one form, titanium hydride can be added to substantially pure titanium, an alloying material and a source of boron such that a mixture of these materials can be compacted and sintered in a powder metallurgy process to produce a component made up of a titanium boride reinforced titanium alloy. In another form, the substantially pure titanium, alloying material and source of boron could be vigorously mixed (with or without the titanium hydride) to such an extent that oxide films that may have built up on the titanium precursor can be removed to minimize the presence of oxygen in the manufactured component.

BACKGROUND OF THE INVENTION

The present invention relates generally to ceramic-reinforced metalalloys, and more particularly to titanium boride-reinforced titaniumalloys and methods of making such alloys.

Powder metallurgy (PM) is a popular way to produce components from awide range of materials, many of which are difficult or impossible toproduce by more conventional approaches, such as casting, forming ormachining. PM is particularly well-suited to making components from bothrefractory materials as well as materials that in other processes thatdo not permit the formation of a true alloy, and is especiallybeneficial in high-volume production (such as automobile componentmanufacturing) due to its repeatability and scrap avoidance attributes.

In a typical PM process, a metal powder is mixed with alloyingmaterials, lubricants, binders or the like, pressed into a near-netshape with appropriate tooling, then sintered in a controlled atmosphereto metallurgically bind the pressed powders together. Frequently, one ormore secondary operations may be undertaken, including deburring andrelated surface treatment, repressing, impregnation and porosityreduction.

Titanium, with is excellent corrosion resistance, relatively hightemperature capability, and high specific strength, is frequently usedin weight-sensitive engineering applications. The transportationindustry, especially that associated with aerospace applications, hasespecially benefitted from the use of titanium and its alloys to createstructurally efficient platforms. Nevertheless, its limited stiffnesshas made it hitherto difficult to fully exploit the advantages titaniumhas to offer relative to its more refractory counterparts. For example,the modulus of elasticity of titanium-based alloys is roughly half ofthat of steel and nickel-based materials. The use of additionalquantities of material to compensate for these lower stiffness valuesreduces the efficiency advantages that titanium enjoys over nickel andiron based alternatives.

One way to increase the stiffness of titanium-based alloys is to combinethem with relatively high modulus ceramic materials. Such coupling of abulk metal with continuous or discontinuous reinforcement is part of arelatively new class of materials known as metal matrix composites(MMCs), where structural properties can be tailored to specificengineering applications by appropriate choice of constituent materials.The discontinuously-configured variant of MMCs in general and oftitanium-based MMCs in particular is amenable to the PM process, ascompound-forming ceramic materials can be reacted with a titanium baseduring sintering to produce reinforcements that improve the propertiesof the composite whole. Specifically, in addition to improving thestiffness of titanium, the reinforcing material, which is typically inparticulate form, provides other structural benefits as well, includingincreased hardness for related wear, and multiple phases for enhancedfracture toughness.

In a PM process for making a titanium-based MMC, a titanium precursorcan be combined with another material that, under proper temperature andpressure conditions, produces hardened, stiff ceramic reinforcingmaterials, such as titanium boride (TiB), titanium carbide (TiC) ortitanium nitride (TiN), just to name a few. Of these, TiB has proven tobe particularly compatible as the reinforcing phase of a titanium MMC,as it exhibits high strength, hardness, heat resistance and modulus ofelasticity, is thermodynamically stable over all of the PM processingconditions of the titanium alloy, is insoluble in the titanium alloy,has similar coefficient of thermal expansion as the titanium alloy, andforms a stable crystallographic boundary between it and the titaniummatrix. Nevertheless, TiB is unstable by itself, so it has to beproduced in situ, such as through reaction of titanium diboride (TiB₂)with titanium powder during sintering.

There are many challenges associated with the production oftitanium-based MMCs by powder metallurgy. The most important factor forhigh quality titanium-based MMCs (or improved fracture toughness andfatigue resistance) is the control of the elements such as carbon,hydrogen, oxygen, nitrogen or the like. It is also important to avoidformation of magnesium and sodium compounds. Among the elements, oxygenis the most important element to be limited. For example, residualoxygen, in the form of an oxide film, may form on the surface of thetitanium precursor. The presence of such oxygen can result in lowerdensity and mechanical properties in the final product, by limiting theproduction of the more desirable reinforcing phases such as theaforementioned diboride. Proper mixing of the powder is also crucial toobtain a homogeneous microstructure, and prevent necklacing of thereinforcing constituent.

There exists a need for high strength titanium-based materials that alsoexhibit excellent toughness, corrosion resistance and high stiffness,wear resistance and heat resistance. There further exists a need toproduce these materials in a cost effective way for high-throughputcomponent manufacturing approaches.

BRIEF SUMMARY OF THE INVENTION

These needs are met by the present invention, wherein a method anddevice that incorporates the features discussed below are disclosed. Inaccordance with a first aspect of the present invention, a method ofmaking a composite component is disclosed. The component is a compositemade from a titanium alloy matrix and TiB₂ reinforcement particlesdispersed within the matrix, where the method includes mixing numerousprecursor (i.e., constituent) materials together to form a mixture,compacting the mixture and sintering the compacted mixture to producethe component in its composite form. The precursor materials includesubstantially pure titanium (for example, elemental titanium), titaniumhydride (TiH₂), an alloying material and a boron source material. Heatgenerated during the sintering process causes the boron source materialto react with the titanium to produce titanium diboride (for example, asa compound in particulate form), while the TiH₂ becomes activated toreact with (and thereby help remove) any oxygen present in the mixture.The TiB₂ reacts with the elemental titanium during sintering to produceTiB, which is only thermodynamically stable in the titanium alloy. TheTiB acts as the reinforcing particulate in the MMC. Sintering, as usedin the present context, is understood as being distinct from otherhigher temperature operations that involve melting, in that sinteringinvolves heating the material to a temperature slightly below (typicallyaround, but not limited to, eighty percent of) its melting point suchthat the disparate particles of the precursor material to adhere to oneanother by solid-state diffusion. Likewise, the term “compacting” andits variants are used synonymously with pressing, where rigid mechanicaltooling can be used to impart a significant pressure on the mixture togive it a preferred geometric shape. By way of non-limiting example,such pressing or compacting operations may involve between five and onehundred tons per square inch of pressure.

Optionally, the precursor materials are in powder form. In such case, asubstantially pure form of titanium powder may be used. In the presentcontext, the term “substantially” refers to an arrangement of elementsor features that, while in theory would be expected to exhibit exactcorrespondence or behavior, may, in practice embody something less thanexact. As such, the term denotes the degree by which a quantitativevalue, measurement or other related representation may vary from astated reference without resulting in a change in the basic function ofthe subject matter at issue. For example, commercially availabletitanium is readily available with purity levels of 99.9 percent, and assuch may be considered to be substantially pure. In addition, oxidationof a substantially pure metal such as titanium does not detract from itssubstantially pure nature. Thus, a substantially pure titanium that hasan oxide film, layer or the like form on the metal surface upon exposureto the ambient atmosphere is still considered to be a substantially puretitanium in the present context.

More specifically, the diameter of the constituent titanium powder isbetween nine and seventy five micrometers, with a typical range betweeneighteen and twenty eight micrometers. The typical range of the alloyingmaterial powder is in the range of five to seventy five micrometers.Similarly, the typical range of the produced TiB₂ powder is in the rangeof five to seventy five micrometers. While it will be appreciated bythose skilled in the art that numerous titanium matrices may be used,there are certain alloys that have demonstrated particular suitabilityfor structural components such as those encountered in aerospace andautomotive applications. These include beta titanium, alpha-2 titanium,gamma titanium and combinations thereof. Examples of beta titanium whichmay be used in the present invention include titanium with approximatelysix weight percent aluminum and approximately four weight percentvanadium (i.e., Ti 6-4), and titanium with approximately six weightpercent aluminum, approximately two weight percent tin, approximatelyfour weight percent zirconium and approximately two percent molybdenum(i.e., Ti 6-2-4-2). The present inventors have found Ti 6-4 to beespecially useful in the manufacture of composite-reinforced automotivecomponents, based on its relative abundance, chemical compatibility andease of processing. Examples of alpha-2 and gamma titanium includeintermetallics, including TiAl and Ti₃Al. The alloying materialdiscussed above may be an aluminum-vanadium powder, which may includevarious approximate ratios including, but not limited to sixty percentaluminum to forty percent vanadium, fifty percent aluminum to fiftypercent vanadium and forty percent aluminum to sixty percent vanadium.

In a particular form, the boron source material may be made up of TiB₂.In another option, the mixture may include up to approximately tenpercent by weight TiH₂, with a more particular range being betweenapproximately three and seven percent by weight titanium hydride.Heating that occurs during the sintering process is preferably limitedto a rate of up to five degrees Celsius per minute, with a moreparticular range being between two and five degrees Celsius per minute.The presently disclosed sintering operation may preferably by performedin a controlled atmosphere to avoid oxidation and related contamination.Examples of such control may include evacuated or inserted environments.

In another option, the process of mixing can serve two purposes. Inaddition to the primary benefit of evenly distributing the powder orother constituents, the inventors have determined that a more aggressivemixing approach helps to strip away oxide layers that may have built upon the surface of the titanium during the exposure of the metal to theatmosphere or related oxygen-containing environment. In this way, themixing further comprises removing at least a portion of suchoxygen-based material. More particularly, the removing comprises placingthe precursor materials in an inert environment (for example, argonafter oxygen evacuation) and subjecting them to rotational mixing untilsuch time as the mixed materials have predetermined characteristics,such as a maximum powder size, surface smoothness, evidence ofpre-sintering alloying, as well as tap density increases, where thelatter corresponds to the bulk density of the mixed material afterhaving been shaken or compacted to promote settling. The rotationalmixing may more specifically include using rotational speeds ofagitators, a mixing drum or other mixing member at high rotationalspeeds for extended lengths of time. The inventors have found thatrotational speeds of approximately 3600 revolutions per minute forbetween approximately four and twelve hours produces the degree ofmixing necessary to effect one of the aforementioned predeterminedcharacteristics, oxygen film removal, or both.

The present invention is well-suited to producing numeroustitanium-based structural components, although the present inventorshave found them to be particularly appropriate for automotive andrelated transportation components. In the present context, the term“automotive” is intended to refer to not only cars, but trucks,motorcycles, buses and related vehicular modes of transportation. Withinthe group of automotive applications, the inventors have found thatcomponents made from the materials and methods disclosed herein areespecially useful in engine-related applications, where high mechanicalloading and high temperatures are both in existence. Examples ofautomotive component uses include valves, retainers, valve springs,connecting rods, bolts, fasteners, coil suspension springs and exhaustsystems.

In addition to the mixing, compacting and sintering operations discussedabove, other optional steps may be undertaken. For example, one or moresurface-modifying operations, such as deburring, surface compressivepeening, porosity reduction or impregnation (the last to introducelubricants into the component such as may be used in bearings, journalsor related friction-reducing parts), may be undertaken to improve thefunctionality of the finished component.

According to another aspect of the invention, a method of preparing amaterial for powder metallurgy processing is disclosed. The methodincludes placing numerous precursor powder materials comprisingsubstantially pure titanium, titanium hydride, an alloying material anda boron source material into a titanium-based mixing container,substantially replacing an ambient atmosphere in the mixing containerwith an inert fluid, rotating an agitator at a minimum predeterminedspeed for a minimum predetermined time until a mixture evidences atleast a twenty percent reduction in powder size, at least a thirtypercent increase in tap density of the mixture, or a substantial removalof an oxide film from the titanium powder. After completion of themixing, the mixture is sintered.

Optionally, the agitator can be configured in various forms. In oneform, the agitator is made up of numerous titanium-based spheres orballs that can be made to rotate within the mixing container, such as bycontainer movement or the like. In another form, the agitators can bepaddles, bars or related members that radially extend from an elongaterotating shaft such that upon shaft rotation, chums powder. In apreferred option, the minimum predetermined rotational speed of thespheres or members is approximately 3600 rotations per minute (RPM), andthe minimum predetermined time is approximately four hours.

According to another aspect of the invention, a method of making atitanium boride reinforced titanium-based metal matrix compositecomponent is disclosed. The method includes mixing at least asubstantially pure titanium powder with an alloying material and a boronsource material. The degree of mixing is similar to that previouslydiscussed, where the mixing is more vigorous than that required for themere substantially even distribution of the constituent materials inthat by the frictional rubbing action between colliding materials inpowder form, most or all of any oxide layers that may have formed on thetitanium powder is removed. In addition to mixing, the mixture must becompacted into a shape of the component, after which the compactedmixture is sintered to a degree sufficient to have the boron sourcematerial react with the titanium to produce a reinforcing phase made upof the titanium boride.

In one optional form, the method further includes adding titaniumhydride to the titanium powder, alloying material and boron sourcematerial constituents such that it can be mixed along with them.Additional steps may include conducting one or more of forging andannealing operations once the component has been sintered.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of the present invention can be bestunderstood when read in conjunction with the following drawings, wherelike structure is indicated with like reference numerals and in which:

FIG. 1 shows a process route flowpath for producing a titanium-based MMCcomponent according to an aspect of the present invention;

FIG. 2 shows the hydrogen content in a titanium-based MMC as a functionof sintering temperature;

FIG. 3 shows a simplified view of equipment used in mixing theconstituent materials used to make the titanium-based MMC;

FIGS. 4A through 4C show various precursor materials after an aggressivemixing process according to an aspect of the present invention;

FIGS. 5 and 6 show exemplary size distributions of titanium powder forTP325 and TP250, respectively;

FIG. 7 shows the results of an x-ray diffraction analysis showing theconversion of TiB₂ to TiB upon sintering;

FIG. 8 shows a scanning electron microscope (SEM) image of an Al—Valloying powder;

FIG. 9 shows a size distribution of the Al—V alloying powder of FIG. 8;

FIGS. 10A through 10D show the microstructure of a sintered Ti MMCaccording to an aspect of the present invention;

FIGS. 11A through 11F show the microstructure of a sintered Ti MMCaccording to an aspect of the present invention using differentprocesses;

FIGS. 12A and 12B show the microstructural dependence of a sintered TiMMC upon various forging temperatures; and

FIGS. 13A and 13B show the microstructural dependence of a sintered TiMMC upon various amounts of added TiB₂.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, the mixing, compacting and sinteringsteps, as well as optional post-sintering steps, are shownschematically. The first step involves mixing 100. As shown, at leastfour different constituent materials are used, including elementaltitanium or other substantially pure form of titanium 110, titaniumhydride 120, an alloying material 130 and a boron source material 140.There are numerous approaches known to those skilled in the art tomixing constituent materials; some such methods include ball millmixing, vibration mill mixing and V-type mixing. These conventionalmethods are generally suitable for their intended purpose, viz. therelatively even distribution of the precursor materials in a mixture ofsuch materials.

Referring next to FIG. 3, the present inventors have discovered thatmodifications to these conventional mixing approaches can be employed toimprove the properties of the mixed precursors, specifically as itrelates to powder size reduction, surface smoothness, slightpre-sintering alloying and increases in tap density of the mixture. Bysignificantly increasing a combination of mixing time and aggressiveness(where the latter can be analogized to shaking the constituents muchmore vigorously than otherwise required to merely achieve theaforementioned even mixing), the present inventors have discovered thatnot only are some of the above attributes realized, but also thatpotentially undesirable oxide layers that may have formed on the surfaceof the titanium powder may be stripped away due to the mechanicalfriction between agitated powers. Such vigorous mixing (through, forexample, a modified milling process) also acts as an activation step, inthat removal of such oxide layers may be advantageous in that it reducesporosity levels, corrosion susceptibility and possible subsequentcontamination of the intended TiB reinforcing phase. In addition, thepresent inventors have determined that the high-speed agitation,especially when performed by various sizes of titanium spheres, is goodat producing the kind of surface deformation of the constituentmaterials that leads to high surface energy levels, which leads todislocation formation and disorder in the resulting crystallographicstructure, thus minimizing crack propagation mechanics.

The inventors have discovered that a modified mechanical pulverizationtreatment (MPT) is beneficial in that it promotes tap and final density.One example of a simplified set of process conditions associated withMPT that the inventors have used includes (1) evacuating and thenproviding argon protection (with pressure higher than atmosphere) to thepowder in the chamber, (2) cooling the chamber to keep the powdertemperature no higher than 35 C, (3) providing a weight ratio of 1:12for the balls and powder materials respectively, (4) providing a ratioof ball sizes of 3:3:1 for ball diameters of 20 mm, 10 mm and 8 mmrespectively, and (5) subjecting the powder to a grinding time ofbetween 4 and 12 hours at a speed of 3600 RPM. These steps should (1)produce powder size decreases by 20 to 60 percent, (2) result in a moresmooth powder surface, (3) promote pre-alloying and (4) increasing tapdensity between 30 and 40 percent with sintering density increasescommensurate with MPT treatment time.

The figure depicts the operation of a mixing device as used in thepresent invention is shown. Mixing device includes a mixing drum orsimilar container 150, precursor feed line 160 with pump 170, rotatingshaft 180 and agitators 190 rigidly affixed to shaft 180. In the presentinvention, the inventors have discovered that a modified mechanicalpulverization treatment approach works especially well with theprecursor materials in producing a preferred mixture. In one particularform, the mixing process, referred to as process uses a modified MPT,utilizes substantially pure titanium spheres or balls 195 of differentsizes, where the ball diameters can be 20 millimeters, while others are10 millimeters and 8 millimeters. Once the precursor materials areplaced inside the mixing drum 150, the container can be evacuated toremove residual oxygen. Afterwards, argon gas (over 99.999%) or arelated inerting fluid is pumped into the container to a slightlyelevated pressure (for example, up to about 1.2 atmospheres) to preventpowder oxidation. To avoid contamination, the entire interior of thecontainer is made of substantially pure titanium, while a coolant, suchas cooling water pumped through coolant circuit 155, can be used to keepthe chamber temperature no higher than 350 C. The weight ratio oftitanium balls to the process powders is 1:12. The mixing is conductedat 3600 rotations per minute for 4 to 12 hours, with each batch ofprecursor materials being between five and ten kilograms.

The presence of the titanium hydride 120 in the mixture will furtherreduce the presence of oxygen in the sintered component. Moreover, thedecomposition of the titanium hydride produces a fine powder of titaniumthat is beneficial in increasing component density as it fills up theinterstitial spaces between the other mixed powders. The inventors havediscovered that there is a preferred range of TiH₂ addition, as toolittle may not provide enough additional oxygen removal, while too muchmay cause non-uniform cracking during sintering.

As mentioned above, there are numerous ceramic-based titanium compoundsthat may be used as reinforcement of the titanium matrix. Nevertheless,the present inventors have determined that some are better-suited to themanufacture of Ti MMC components than others. For example, TiN is a weakreinforcing phase relative to TiC and TiB, and of these remaining two,the latter worked better. The concentration of thermodynamically stableceramic particles (such as TiB and TiB₂) is chosen based on theapplications. For many automotive applications, the inventors havediscovered that an upper limit may be approximately eighteen percent byweight, with a lower limit of as little as one percent. From phasediagram information, the present inventors expect that the reactionbetween Ti and TiB₂ during sintering process would form thethermodynamically stable phase of TiB in Ti alloys.

The second step employed in making the material includes compacting,pressing or otherwise forming the mixture. This is shown as step 200. Aswith the mixing step discussed above, there are various ways in whichthe component can be formed into its green (i.e., pre-sintered) state.Such ways include isostatic forming, die forming or the like. Thepressure imparted to the mixture during compaction 200 is sufficient tomaintain the part substantially in a near-net shape while awaiting thesintering step 300 (discussed below).

The third step is the sintering step 300. During sintering, thecompacted green component is heated such that the titanium (for example,elemental titanium) and the alloying material are alloyed, therebyproducing the titanium-based matrix. As stated above, controlledenvironments may be used to reduce the likelihood of contamination.Temperatures at which the sintering step 300 may be conducted arepreferably between 1200° C. and 1450° C. The sintering step 300 mayinclude a ramped heating schedule, such as between 2 and 5 degreesCelsius per minute. One example of the effects of sintering temperature,specifically, on the amount of hydrogen present in a Ti-MMC, is shown inFIG. 2.

Afterwards, a cooling schedule may be used, where the sintered componentis cooled over the course of 7 hours. In such circumstance, cooling ratemay be approximately 200° C. per hour. Also during the sintering step300, reactions are taking place between the boron source material 140and the titanium 110 to form TiB, as well as the titanium alloy (forexample, Ti6Al4V). Likewise, the step may also include closed dieforging or phase-transformation densification 400, where small voidsleft over from the sintering process can be removed by using a hot pressforging. Such a step is preferably conducted at a high temperature.Coatings applied to the part at room temperature help to prevent partoxidation at high temperature. In one form, the coating contains Al₂O₃,SiO₂ and B₂O₃, as well as organic binder. It can be applied with a brushfor a few coats when the parts are heated to 70 C, after which the partis dried. Typical forging temperatures range from 900 to 1400 C, andmore particularly between 1200 and 1350 C, depending upon the TiB₂content, with higher levels requiring that a higher forging temperaturebe used. The typical reduction ratio (which is the ratio of the crosssectional area before and after forging, sometimes referred to percentreduction in thickness, and related to the size of the processed MMCmaterial) should be broadly between 300 and 800 percent, with a moreparticular range of 500 to 700 percent. In such a range, the sinteringtemperature would be 1350 C. The typical anneal temperature should bewithin a broad range of 550 to 950 C, and more particularly between650-740 C. The time should be between one half and two hours.

Also as shown in FIG. 1, a closed die forging or relatedphase-transformation densification can also be performed. In this case,hot pressing within a closed die can be used to achieve additional voidremoval and consequent densification. In this case, the sinteringtemperature is 1350 C. The typical anneal temperature should 650-740 C,with a range of 550 to 950 C. The time should be 0.5 to 2 hours. Theprocess of the present invention could result in a high sintered densityof over 99%.

Referring with particularity to FIGS. 4A through 4D, a typical mixedpowder image before and after MPT is shown, where FIG. 4A corresponds topre-MPT titanium powder, FIG. 4B corresponds to pre-MPT TiB₂ powder,FIG. 4C corresponds to pre-MPT alloying powder (specifically,aluminum-vanadium (Al—V) powder) and FIG. 4D corresponds to post-MPTmixed powder. Comparing the powder without MPT treatment, theperformance of MPT treated powder under the aforementioned MPTconditions showed powder size decreases between 20 and 60 percent,increased powder surface smoothness, slightly pre-alloying of some ofthe powder, and increases in tap density of between 30 and 40 percent.The effect of the MPT on the sintered density is shown in the followingtable:

Process time (hours) Density (grams/cm³) 0 3.06 4 3.97 8 4.05 12 4.12

Pre-sintering compaction and related tap density can be achieved bynumerous vibration, shaking or related agitation means. One approach toincreasing the pre-sintering compaction is through cold die compaction.In one form, this can be conducted at room temperature at 190-360 MPa(i.e., approximately 28,000 to 52,000 psi) for 3 minutes, with a typicalrange of 1 to 6 minutes, and a typical pressure range of between 230 and270 MPa. The inventors have discovered that to achieve a best greendensity and green strength, a preferred titanium particle size should be22 and 34 micrometer within a broader range of 5 to 75 micrometers. Thesintering process includes heating these green parts at a rate of 2 to 5degrees Celsius per minute until they reach the desired sinteringtemperature of approximately 1300 degrees Celsius, with a typical range(as mentioned above) of 1200 to 1450 degrees Celsius, for 3 hours, witha typical range 2 to 8 hours. During sintering, it is advantageous tomaintain a vacuum of 10³ Pa for a between 2 and 8 hours, with a morespecific range of 3 to 6 hours in order to achieve 99% theoreticaldensity. Longer sintering times can further improve the sintereddensity.

Precursor material sizes may vary, although the typical sizes of thetitanium powders used for making Ti6Al4V MMC range broadly between 9 and75 micrometers, with a narrower range between 18 and 28 micrometers.There are several possible methods for producing titanium powder. One ofthem is done by a hydride-dehydride titanium powder making process witha varied rotation speed during jet milling to get different powdersizes. Referring with particularity to FIGS. 5 and 6, size distributionand morphology of two typical Ti6Al4V particles are shown, where FIG. 5corresponds to 325 mesh titanium powder, and FIG. 6 corresponds to 250mesh titanium powder.

The typical TiB₂ particle size is in the range of 5 to 75 micrometers,and can be prepared by a self-propagating high-temperaturesynthesis-process, such as that shown in the following reaction:

Ti+2B→TiB₂+Q (324 KJ/mol)

The physical properties of TiB₂ powder are shown in the following table,while FIG. 7 shows an X-ray diffraction analysis that distinguishedbetween pre-sintered (i.e., green) and sintered samples to show how TiBformed from the TiB₂ and titanium sintering reaction. The precursorsused to produce the results depicted in FIG. 7 included powders oftitanium, TiH₂, Al—V 40 alloy and TiB₂. The average TiB₂ particle sizeis 9.2 micrometers, and is approximately 99 percent TiB₂.

Physical Properties Value Density, g/cm³ 4.25 Melting Point, ° C.2850-2980 Thermal Expansion, m/m · k 8.1 × 10⁻⁶ Thermal Conductivity,W/m ° C. 60-120 (at 25° C.)  55-125 (at 2300° C.) Flexural Strength, MPa350-500 Knoop Hardness, GPa 30-34 Electrical Resistivity, p 0 · cm 14.4Modulus of Elasticity, GPa 550

TiB₂ and Ti6Al4V have similar densities. It is advantageous to mix them.However, it has been found that TiB₂ significantly decreases thesintered density of titanium MMC. When the content of TiB₂ is higherthan 7% by weight, the forged density also starts to decreasesignificantly. One possible explanation may be the significantdifference in the relative densities of boron (approx. 2.34 g/cc) andtitanium (4.5 g/cc).

The typical particle size of Al—V alloying material is in the range of 5to 75 micrometers. In powder form, these alloying materials are alsoprepared by a commercially available self-propagating high-temperaturesynthesis-process shown in simplified form according to the followingreaction:

Al+V₂0₅→AIVx+Al₂0₃+Q

Three different Al—V alloy powders were prepared with aluminum tovanadium ratios of 60/40, 50/50 and 40/60 respectively, for makingTi6Al4V MMC. The chemical compositions were primarily aluminum andvanadium with traces amounts of oxygen, carbon, iron and silicon. FIGS.8 and 9 show with particularity the SEM morphology and particle sizedistribution of the 60/40 Al—V powders.

Referring next to FIGS. 10 through 13, the results of various sinteringsteps and weight percentages of TiB₂ are shown. Referring withparticularity to FIGS. 10A through 10D, the sintered microstructure of aTi6Al4V MMC with varying levels of TiB₂ present are shown. The sinteringtemperature was 1300 degrees Celsius, and the TiB₂ is present in 7percent, 10 percent, 15 percent and 20 percent, respectively. Referringwith particularity to FIGS. 11A through 11H, the microstructure due todiffering TiB₂ concentrations and processing conditions are shown. Inparticular, the TiB₂ concentrations varied from 3 percent (FIGS. 11A and11B) to 5 percent (FIGS. 11C and 11D), and 7 percent (FIGS. 11E through11H), and included (in FIGS. 11B, 11D, 11F and 11H) the effect ofadditional processing steps, including forging (at 950 degrees Celsius)and annealing (at 930 C). Referring with particularity to FIG. 10, thepost-sintering microstructures of the MMCs with varied TiB₂ contents areshown. Referring with particularity to FIG. 11, the annealedmicrostructures of the MMCs with varied TiB₂ contents after forging areshown. Comparison of FIG. 10 to FIG. 11 indicates that 10% TiB MMC has adense and clean microstructure. As shown in FIGS. 12A and 12B, changesin the forged temperature impacts the microstructure of the Ti6AI4V/TiBMMC. Likewise, the effect of varying degrees of the TiB₂ boron sourcematerial on sintered, forged and annealed microstructure is shown inFIGS. 13A and 13B. Specifically, they indicate the effect of forging andanneal temperatures on the porosity. For example, from the foregoing, itcan be seen that a forging temperature of 1150 C is much better than 950C on the cracking tendency and porosity level. Referring withparticularity to FIG. 13, the annealed microstructure is shown.

Referring again to FIG. 1, numerous examples of post-sinteringoperations 500 are possible, such as machining (including deburring),surface compressive peening, repressing or the like. Another exampleincludes oxidation-prevention steps. In this case, a coating can beapplied to the finished part at room temperature, where the coatingcontains various oxides, such as Al₂0₃, Si0₂ and B₂0₃, as well as anorganic binder. In one form, the coating can be applied with a brush fora few coats when the parts are heated to a slightly elevatedtemperature, for example approximately 70 C, after which the parts aredried.

Compared to unreinforced Ti6Al4V alloy, the Ti6Al4V MMC discussed hereinhave higher strength and elastic modulus. As such, TiB₂ is an excellentreinforcement for Ti6Al4V titanium alloy. For example, the elasticmodulus of the reinforced Ti6Al4V is over 140 GPa, with an average of155 GPa, in comparison with 100 GPa average for unreinforced Ti6Al4V.The ultimate tensile strength of over 1350 MPa (average 1450 MPa) issignificantly greater than the 1140 MPa average for the unreinforcedTi6Al4V, with a 0.2% yield strength of over 1250 MPa (average 1300 MPa),in comparison with average of 980 MPa for unreinforced Ti6Al4V. TheRockwell hardness is above 43. One example of a structural componentmade according to one of the aspects of the present invention is aconnecting rod for use in an automotive engine, although it will beappreciated by those skilled in the art that numerous other componentsmay also be manufactured.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the invention, which is defined in the appendedclaims.

1. A method of making a composite component that includes a titaniumalloy matrix and a titanium diboride reinforcement, said methodcomprising: mixing a plurality of precursor materials comprisingsubstantially pure titanium, titanium hydride, an alloying material anda boron source material; compacting said mixture; and sintering saidcompacted mixture such that during said sintering, said boron sourcematerial reacts with said substantially pure titanium to producetitanium boride and said titanium hydride becomes activated to reactwith any oxygen present in said mixture.
 2. The method of claim 1,wherein said precursor materials are in powder form.
 3. The method ofclaim 2, wherein said mixing further comprises removing at least aportion of any oxygen-based material formed on a surface of saidsubstantially pure titanium.
 4. The method of claim 3, wherein saidremoving comprises placing said plurality of precursor materials in aninert environment and subjecting them to rotational mixing until suchtime as
 5. The method of claim 4, wherein said rotational mixingcomprises rotational speeds of at least approximately 3600 revolutionsper minute for a duration of at least approximately four hours.
 6. Themethod of claim 1, wherein said matrix is selected from the groupconsisting of beta titanium, alpha-2 titanium, gamma titanium andcombinations thereof.
 7. The method of claim 6, wherein said mixturecomprises between approximately three and seven ten percent by weighttitanium hydride.
 8. The method of claim 1, wherein said heating occursat a rate of up to five degrees Celsius per minute.
 9. The method ofclaim 1, wherein said alloying material comprises aluminum and vanadium.10. The method of claim 1, wherein said boron source material comprisestitanium diboride.
 11. The method of claim 1, wherein said componentcomprises an automotive component.
 12. The method of claim 11, whereinsaid automotive component is selected from the group consisting ofvalves, retainers, valve springs, connecting rods, bolts, fasteners,coil suspension springs and exhaust system.
 13. The method of claim 1,further comprising at least one post-sintering surface-modifyingoperation.
 14. The method of claim 13, wherein said at least onepost-sintering surface-modifying operation is selected from the groupconsisting of deburring, porosity reduction and lubricant impregnation.15. A method of preparing a titanium-based material for powdermetallurgy processing, said method comprising: placing a plurality ofprecursor powder materials comprising substantially pure titanium,titanium hydride, an alloying material and a boron source material intoa titanium-based mixing container; substantially replacing an ambientatmosphere in said mixing container with an inert fluid; rotating anagitator at a minimum predetermined speed for a minimum predeterminedtime until a mixture possessing at least one of the following isachieved: (1) at least a twenty percent reduction in powder size; (2) atleast a thirty percent increase in tap density of said mixture; and (3)a substantial removal of an oxide film from said titanium powder; andsintering said mixture.
 16. The method of claim 15, wherein saidagitator comprises a plurality of titanium-based spheres configured torotate within said mixing container.
 17. The method of claim 15, whereinsaid minimum predetermined speed is approximately 3600 rotations perminute, and said minimum predetermined time is approximately four hours.18. A method of making a titanium boride reinforced titanium-based metalmatrix composite component, said method comprising: mixing at least asubstantially pure titanium powder with an alloying material and a boronsource material such that a substantial majority of any oxide forming onsaid substantially pure titanium powder is removed therefrom; compactingsaid mixture into a shape of said component; and sintering saidcompacted mixture such that during said sintering, said boron sourcematerial reacts with said substantially pure titanium to produce areinforcing phase made up of said titanium boride.
 19. The method ofclaim 18, further comprising adding titanium hydride to saidsubstantially pure titanium powder, alloying material and boron sourcematerial prior to said mixing.
 20. The method of claim 18, furthercomprising at least one of forging and annealing said component oncesaid sintering is completed.